1. Field of the Invention
The present invention relates to an electric power-steering apparatus motor apparatus that is mounted to an automotive vehicle to assist steering effort by a driver, for example.
2. Description of the Related Art
Conventional pumping devices that supply oil to electric power steering apparatuses include: a heat sink is configured into a hollow shape by joining together with and fixing to a flat first member a first end surface of a second member that is formed into a vessel shape in which a first end surface is open; a motor that is mounted by joining together and fixing a motor frame to an outer surface of the first member; a pumping unit that is mounted to an outer surface of the second member; and a control unit that is joined together with and fixed to an inner surface of the second member of the heatsink where the pumping unit is disposed, and that controls driving of the motor. A first end portion of a rotating shaft of the motor is rotatably held by a first bearing that is disposed inside the motor frame, and an intermediate portion thereof is rotatably held by a second bearing that is disposed in a penetrating aperture that is formed on the first member. In addition, a second end portion of the rotating shaft projects through a penetrating aperture that is formed on the second member, and is linked to a drive shaft of the pumping unit by means of a coupling such that the pumping unit is driven by the rotating shaft of the motor and circulates oil (see Patent Literature 1, for example).
In conventional pumping devices, an inclination generally arises in a central axis of the rotating shaft that is determined by the first bearing and the second bearing relative to a central axis of the drive shaft of the pumping unit that is mounted to the outer surface of the second member due to core misalignment due to dimensional tolerances and combinations of parts, etc.
In conventional pumping devices, because the first end portion of the rotating shaft of the rotor is rotatably held by the first bearing that is disposed inside the motor frame, and the intermediate portion is rotatably held by the second bearing that is disposed on the first member, and a second end region passes through the heatsink and projects from the penetrating aperture that is formed on the second member, axial length between the second bearing and the coupling that is disposed on the second end of the rotating shaft is increased. Thus, one problem has been that vibration of the coupling is increased, increasing vibration of the pumping unit, and reducing reliability.
Because an outside diameter of the second end region of the rotating shaft that projects out through the second bearing is smaller than an inside diameter of an inner ring of the second bearing, rigidity of the second end region of the rotating shaft is reduced, and one problem has been that vibration and torque response lag arise due to torsion resonance, reducing reliability. In order to solve this problem, it is conceivable that the diameter of the second end region of the rotating shaft could be increased to increase rigidity, but in that case, it would be necessary to increase the diameter of the second bearing, giving rise to new problems such as enlargement of the device and cost increases.
Another problem has been that foreign matter may enter the heatsink through gaps between the second end region of the rotating shaft and the penetrating aperture that is disposed on the second member, giving rise to short-circuiting of the control unit, and reducing reliability.
In consideration of these conditions, conventional electric power steering apparatuses have been proposed in which a control apparatus is disposed in a space that is made by placing a first end of a first housing and a first end of a second housing in contact with each other, a motor is disposed inside a frame that is mounted to a second end of the first housing, an actuator is disposed at a second end of the second housing, a first end region of a rotating shaft of the motor is rotatably held by a first bearing that is disposed in a penetrating aperture that is formed on the second housing, a second end portion of the rotating shaft is rotatably held by a second bearing that is disposed in the frame, and a first end portion of the rotating shaft that projects out through the first bearing is linked with a drive shaft of the actuator by means of a coupling (see Patent Literature 2, for example).
In conventional electric power steering apparatuses, because the actuator is disposed at the second end of the second housing, and the drive shaft thereof is linked by means of the coupling to the first end portion of the rotating shaft of the motor that projects out through the first bearing that is disposed in the penetrating aperture that is formed on the second housing, axial length between the first bearing and the coupling that is disposed on the first end of the rotating shaft is shortened. Thus, vibration of the coupling is suppressed, reducing vibration of the actuator, and increasing reliability.
Portions of the rotating shaft between the first and second bearings are thickened, enabling rigidity of the rotating shaft to be increased without increasing the diameters of the first and second bearings, suppressing vibration and torque response lag due to torsion resonance, and enabling reliability to be increased.
In addition, because the two ends of the rotating shaft are held by the first and second bearings, foreign matter is less likely to enter the space that is made by placing the first end of the first housing and the first end of the second housing in contact with each other, suppressing occurrences of short-circuiting of the control apparatus, and increasing reliability.
Patent Literature 1: Japanese Patent No. 3830006 (Gazette)
Patent Literature 2: Japanese Patent Laid-Open No. 2006-121857 (Gazette)
In conventional electric power steering apparatuses, because the first bearing is inserted into and held by the bearing box of the second housing from a first housing side, a first bearing axial positioning wall portion of the bearing box is positioned between the first bearing and the actuator. Thus, because a distance between the first bearing and the first end of the rotating shaft is extended by a distance equivalent to the thickness of the first bearing axial positioning wall portion, one disadvantage has been that vibration of the coupling is increased, increasing vibration of the actuator, and giving rise to reductions in reliability.